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Re: [PATCH] xfstests: kill lib/random.c

To: Ben Myers <bpm@xxxxxxx>, Eric Sandeen <sandeen@xxxxxxxxxx>, Josef Bacik <jbacik@xxxxxx>
Subject: Re: [PATCH] xfstests: kill lib/random.c
From: Eric Sandeen <sandeen@xxxxxxxxxxx>
Date: Tue, 07 Jan 2014 14:15:05 -0600
Cc: linux-btrfs@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <52CC5F27.1090602@xxxxxxxxxxx>
References: <1389038323-8304-1-git-send-email-jbacik@xxxxxx> <52CB20ED.1010705@xxxxxxxxxx> <52CB2336.2060009@xxxxxx> <52CB2452.70507@xxxxxxxxxx> <20140107200135.GD1935@xxxxxxx> <52CC5F27.1090602@xxxxxxxxxxx>
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On 1/7/14, 2:10 PM, Eric Sandeen wrote:
> On 1/7/14, 2:01 PM, Ben Myers wrote:
>> Hey Gents,
>>
>> On Mon, Jan 06, 2014 at 03:46:58PM -0600, Eric Sandeen wrote:
>>> On 1/6/14, 3:42 PM, Josef Bacik wrote:
>>>>
>>>> On 01/06/2014 04:32 PM, Eric Sandeen wrote:
>>>>> On 1/6/14, 1:58 PM, Josef Bacik wrote:
>>>>>> I was trying to reproduce something with fsx and I noticed that no 
>>>>>> matter what
>>>>>> seed I set I was getting the same file.  Come to find out we are 
>>>>>> overloading
>>>>>> random() with our own custom horribleness for some unknown reason.  So 
>>>>>> nuke the
>>>>>> damn thing from orbit and rely on glibc's random().  With this fix the 
>>>>>> -S option
>>>>>> actually does something with fsx.  Thanks,
>>>>> Hm, old comments seem to indicate that this was done <handwave> to make 
>>>>> random
>>>>> behave the same on different architectures (i.e. same result from same 
>>>>> seed,
>>>>> I guess?)  I . . . don't know if that is true of glibc's random(), is it?
>>>>>
>>>>> I'd like to dig into the history just a bit before we yank this, just to
>>>>> be sure.
>>>>
>>>> I think that if we need the output to match based on a predictable
>>>> random() output then we've lost already. We shouldn't be checking for
>>>> specific output (like inode numbers or sizes etc) that are dependant
>>>> on random()'s behaviour, and if we are we need to fix those tests. So
>>>> even if that is why it was put in place originally I'd say it is high
>>>> time we ripped it out and fixed up any tests that rely on this
>>>> behaviour. Thanks,
>>>
>>> Yeah, you're probably right.  And the ancient xfstests history seems to
>>> be lost in the mists of time, at least as far as I can see.  So I'm ok
>>> with this but let's let Dave & SGI chime in too just to be certain.
>>
>> I did not have success locating the history prior to what we have posted on
>> oss.  I agree that it was likely added so that tests that expose output from
>> random into golden output files will have the same results across arches.
>> Maybe this is still of concern for folks who use a different c library with 
>> the
>> kernel.  
>>
>> Looks there are quite a few callers.  IMO if we're going to remove this we
>> should fix the tests first.
> 
> Or first, determine if they really need fixing.  Did you find tests which
> actually contain the random results in the golden output?

This should be easy enough to test by just hacking the lib/random.c with a
new starting seed, right?

-Eric

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